Packrat Middens
Packrats ' The bushy-tailed woodrat is a common rodent found in Canada and the United States, and are the species found in Chaco Canyon. It is know as the original "packrat" as it shows strong preference towards shiny objects, often dropping whatever food they have in their mouths to pick up a shiny coin. Bushy-tailed woodrats can be identified by their large, rounded ears, and their long, bushy tails. They are usually brown, peppered with black hairs above with a white underside and feet. The top coloration may vary from buff to almost black. The tail is squirrel-like; bushy, and flattened from base to tip. The adult lenght of the woodrat is 11 to 18 in, half of which is tail, and weighs up to 1.3lbs. '''Middens ' Their preferred habitat is in and around rocky places, so they often are found along cliffs, canyons, and open rocky fields. Inorder to protect their nests they construct debris piles infront of the openings, these piles are called middens. The middens may be analyzed to reconstruct the original environment 0-100m around the nest. The reconstruction can then be comparted to the current environment of the area. The woodrats often urinate on the debris piles, as the urine drys, sugars and other substances in the urine crystallize. This creates a material know as amberat, which cements the debris together. The urine as well as the dry climate of the American Southwest dramtically slows the decay of the debris, and the location often protects the midden from the elements. These piles were often made up of plant materials, feces, and airborne particulates that are trapped in the urine. A woodrat midden may preserve the materials incorporated in it for up to 50,000 years, according to radiocarbon dating. As well as the environment that the woodrat lived in the midden can also be used to determine the size of the rodent, which according to Bergmanns rule we can predict climate. '''Dendrochronology Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. A horizontal cross section is cut through the trunk of a tree, visible rings result from the change in growth speed through the seasons of the year. 'Analysis ' According to Bergmann's rule, the body size of vertabrates is closely related to the average ambient air temperature in the region which the vertabrate lives. Organisms in warmer regions are typically smaller to dissapate heat more efficiently while in smaller regions are typically larger inorder to conserve heat. Among the debris in the midden are fecal pellets. The size of the pellet is proportional to the size of the woodrat. By measuring the pellets, the approximate size of the woodrat is determined based on a study of field-trapped woodrats. From Bergmann's rule the differences in climates can be determined. Analysis of the midden are preformed in multiples steps. First the midden is disaggregated in water. The water is then collected and ran through a mass spectrometer to detect pollen and other particulates dissolved in the urine. The fossilized plant materials are then separated by microscope and classified. Early middens from Chaco Canyon, New Mexico and a terminal Pleistocene midden from Canyon de Chelly, Arizona, show that Blue spruce, Limber pine, Douglas fir, Dwarf juniper, and Rocky Mountain juniper which is now a deserted region no longer containing these tree species. The packrat middens were important in helping to determine that the landscape where the Anasazi society once thrived was once covered with forests. Today this area is a high-desert landscape, with long winters, short growing seasons, and marginal rainfall. These factors create an unlikely place for a major center of an ancient culture to take root and flourish. Dendrochronology was also used to establish the time that the Chaco Canyon was populated by the Anasazi society. This study examines the use of a large sample of structural wood to place the site in its temporal framework as well as examine the organizational control exhibited by the need for structural wood and its possible relationship to other contemporary sites in the Chaco Canyon core. 'Sources ' "Bushy-tailed Woodrat - Neotoma cinerea". eNature.com. Trapani, Josh (2003). "Neotoma cinera" Animal Diversity Web. http://www.ncdc.noaa.gov/paleo/slides/slideset/16 Journal of Arid Environments, Using Packrat Middens to assess grazing effects on vegetation change, 10.1016, J. Fisher, K.L Cole, R.S. Anderson http://www.nps.gov/chcu/historyculture/index.htm http://cat.inist.fr/?aModele=afficheN&cpsidt=23026481